Electromagnetic clutch-brake devices

ABSTRACT

A combination magnetic particle clutch and brake device comprising a rotatable output shaft having a single magnetic coupling member mounted thereon for rotation therewith, the coupling member comprising a hollow cylindrical portion having an axis of rotation substantially coincidental with, the axis of rotation of the shaft and an annular portion extending substantially radially of the cylindrical portion. The brake section of the device includes a stationary magnetic armature and one of the portions of the member, while the clutch section includes a rotor and a stator and the other of the portions of the member. Means connect the stationary armature and the stator as a unit. Driving coils are provided for establishing magnetic flux paths through the armature and one portion of the coupling member and through the rotor and stator and the other portion of the coupling member. The armature and the rotor are spaced from and surround the coupling member so as to define a single continuous space which is filled with magnetic particles. Sealing means are provided for substantially preventing magnetic particles from escaping from the space.

United States Patent Hendershot June 27, 1972 [54] ELECTROMAGNETICCLUTCH-BRAKE DEVICES [72] Inventor: James R. Hendershot, Amherst, NH.

[73] Assignee: Vibrac Corporation, Chelmsford, Mass.

[22] Filed: Sept. 4, 1970 [211 App]. No.: 69,839

Primary Examiner-William F. ODea Assistant Examiner- Randall HealdAttorney-Schiller & Pandiscio [57] ABSTRACT A combination magneticparticle clutch and brake device comprising a rotatable output shafthaving a single magnetic coupling member mounted thereon for rotationtherewith, the coupling member comprising a hollow cylindrical portionhaving an axis of rotation substantially coincidental with, the axis ofrotation of the shaft and an annular portion extending substantiallyradially of the cylindrical portion. The brake section of the deviceincludes a stationary magnetic armature and one of the portions of themember, while the clutch section includes a rotor and a stator and theother of the portions of the member. Means connect the stationaryarmature and the stator as a unit. Driving coils are provided forestablishing magnetic flux paths through the armature and one portion ofthe coupling member and through the rotor and stator and the otherportion of the coupling member. The armature and the rotor are spacedfrom and surround the coupling member so as to define a singlecontinuous space which is filled with magnetic particles. Sealing meansare provided for substantially preventing magnetic particles fromescaping from the space.

18 Claims, 2 Drawing Figures PATENTEDJUHZT m2 3,672,476

SHEET 1 or 2 JAMES R HENDERSHOT lA/VE/VTOR.

By .SZAi/r 9 pan$5cl0 ATTORNEYS,

PATEMTEnJum m2 SHEET 2 OF 2 WWW Vm W

vQm Wm W vmW mw Qmw W WmW WNW knm mum WWW RUM WWW kWW

VWW QM W WWW WWW

l/A MES R HENDERSHOT //V V E N 7 0R.

WMMW

SAM/er 9 p w ATTORNEYS.

ELECTROMAGNETIC CLUTCH-BRAKE DEVICES This invention relates to magnetictorque transmitting devices and more particularly to those devicesemploying magnetic particles in a combined clutch and brake assembly.

Magnetic particle devices of various types are well known to the art.Most commonly they are constructed to function as quick-acting,electrically actuated clutches or brakes. Combination magneticallyenergized clutch and brake devices are also known in the art and areextremely useful in providing quick-response, selectively energizablecombination clutch and brake units which may be employed, for example,in a tape drive mechanism. The present invention is concerned with animprovement that greatly simplifies the construction and assembly, aswell as the accuracy and reliability of such combination magneticparticle clutch and brake assemblies. Typically prior devices of thetype to which the invention relates consist of a single rotatablymounted output shaft having two or more coupling members in the form ofradially extending discs that rotate therewith. The brake assembly ofsuch prior devices consists of first and second stationary membersmounted about one of the discs with a spacing therebetween which isfilled with magnetic particles, plus a coil to selectively establish amagnetic flux between the stationary members and the disc in order tomagnetically lock the particles and prevent relative rotation betweenthe disc and the stationary magnetic members. The clutch assembly ofsuch devices comprises a rotor structure mounted about but spaced fromanother of the discs, with the intervening spaces being filled withmagnetic particles. The clutch assembly is provided with a coil toselectively establish a magnetic flux between the rotor structure andthe associated disc in order to lock the particles intotorque-transmitting chains coupling the disc and rotor structure. Therotor serves as an input or driving member to impart rotation to theoutput shaft when the clutch coil is energized. Bearing assemblies areprovided at the ends and intermediate the ends of the unit forpermitting rotation of the rotor structure and the output shaft. Sealingmeans are provided for preventing the escape of particles from thespaces. Because of the construction of such prior art devices at leastfour sealing members are usually required. Such prior devices arerelatively large and are too expensive for use in mini-computers andother computer peripheral equipment where size and cost as well aslifetime are critical factors.

Accordingly, an object of the present invention is to provide acombination magnetic particle clutch and brake assembly which isrelatively simple to construct and assemble.

Another object of this invention is to provide a combination magneticparticle clutch and brake assembly which is very small and compact.

Still another object of the present invention is to provide acombination magnetic particle clutch and brake assembly which isrelatively inexpensive compared to other combination magnetic particleclutch and brake devices.

Yet another object of the present invention is to provide a combinationmagnetic particle clutch and brake assembly which is especially suitedfor use in mini-computers and other computer peripheral equipment.

A further object of the present invention is to provide a combinationmagnetic particle clutch and brake device in which a single integralcoupling member, which may be stamped or drawn, serves both the clutchand brake stages.

Another object of the present invention is to provide a combinationmagnetic particle clutch and brake assembly which has only a singlecontinuous magnetic-particle-filled space for both the clutch and brakeunits.

Still a further object of the present invention is to provide acombination magnetic particle clutch and brake assembly in which thebrake gap may be inspected during assembly for proper spacing.

Yet a further object of the present invention is to provide acombination magnetic particle clutch and brake assembly which requiresonly two seals of simple construction, rather than the usual four, forpreventing particles from escaping from the magnetic-particle-filledspace.

The above objects, advantages and features of the present invention, aswell as others, may be accomplished by providing in a combinationmagnetic particle clutch and brake device having rotatable input andoutput shafts, a brake unit including a stationary magnetic annature, aclutch unit including a rotor and a stator, means connecting thearmature and the stator as a unit, and driving coils for establishingmagnetic flux paths for the clutch unit and the brake unit, theimprovement comprising a novel single magnetic coupling member mountedon one of said shafts for rotation therewith. The coupling membercomprises two portions, one serving the brake unit and the other servingthe clutch unit. The coupling member is shaped and disposed so as toprovide spaces between adjacent cooperating portions of the clutch andbrake unit which are filled with magnetic particles. The magnetic fluxestablished by the brake coil has a path through the magnetic particles,the armature and one of the portions of the coupling member, while theflux established by the clutch coil has a path through the magneticparticles, the rotor and stator and the other of the portions of thecoupling member. Only two resilient seals are required to preventleakage of the magnetic particles. Other objects and many of theattendant advantages of this invention are believed to be apparent fromthe following specification which is to be considered together with theaccompanying drawings, wherein:

FIG. 1 is a longitudinal partial sectional view of a combinationmagnetic particle clutch and brake assembly constituting a preferredembodiment of the present invention; and

FIG. 2 is a longitudinal partial sectional view of a combinationmagnetic particle clutch and brake assembly constituting an alternativeembodiment of the present invention.

Turning now to FIG. 1 there is illustrated a combination magneticparticle clutch and brake device 10 comprising a cylindricalclutch/brake stator housing 12 providing at one end 14 thereof a supportfor a rotatable input shaft 16 having an axis of rotation 17. Housing 12is made of non-magnetic material. The other end 18 of housing 12provides a support for an output shaft 20. End 18 has an opening 22therein which is used as a mounting pilot for the assembly 10.

A pair of annular field coils 30 and 32 each wound around bobbins 34 and36 respectively and of known construction are secured in housing 12. Anannular magnetic sleeve 33 extends axially around both coils 32 and 34along the inner wall of housing 12. Both bobbins 34 and 36 abut opposingfaces of an intervening annular ring 38 which extends inwardly from thewall of housing 12. Ring 38 has a portion 39 that projects inwardlytoward axis 17 further than the rest of ring 38. Bobbin 34 is held inabutting position with one face of ring 38. Bobbin 36 is held inabutting position with another face of ring 38 opposite that againstwhich bobbin 34 abuts. Ring 38 is made of magnetic'material and alsofunctions as a stator pole. The opposite ends of coils 30 and 32 areeach connected to pairs of leads 42 and 44 respectively which projectout of housing 12 through suitable openings 46 and 48 respectively.Leads 42 and 44 are used to couple coils 30 and 32 to an external powersource (not shown) whereby they may be energized.

The input stage of the device includes an input rotor 50 at the innerend of input shaft 16. The latter is made of magnetic material and itsouter end has a keyway 51 formed on the outer surface thereof whichallows it and rotor 50 to be cou' pled to a source of torque input. Withrespect to the rotor 50, the shaft 16 is formed with a peripheral flange52 and a reduced diameter cylindrical extension 54 on which is affixedan annular spacer 56 which is L-shaped in longitudinal section. Spacer56 engages flange 52. Afiixed to spacer 56 is a cylindrical member 58which is spaced radially from extension 54. Spacer 56 and member 58 maybe secured to each other and to shaft 16 by a press fit or by othersuitable means. The free end of member 58 (which forms part of rotor 50)has a bull-nose extension 61 on one end thereof. Bull-nose extension 61has a substantially rounded end but other configurations may be employedsuch as a flat end, a saddled end, etc.

The function of bull-nose extension 61 will be explained later. Thecylindrical member 58 is made of the same magnetic material as shaft 16so that it and extension 54 can function as armature members or poles.of the clutch, while spacer 56 is made of a non-magnetic material. Themember 58 and shaft extension 54 have confronting axially extendinginner and outer surfaces 62 and 63 respectively, which are spaced fromone another as a result of spacer 56 to define an axially extendingspace or gap 64 and function as poles to direct a magnetic field througha selected portion of the output stage of the clutch unit. Mountedwithin housing 12 concentric with but spaced from flange 52 of shaft 16is an annular member 65 which is made of magnetic material and functionsas a stator pole. At this point it is to be noted that sleeve 33functions as part of the stator of the clutch unit and part of the brakeunit. One side of member 65 engages and holds bobbin 34 against theadjacent side surface of the inwardly extending ring 38.

Shaft 16 is rotatably supported in housing 12 by means of a bearingassembly comprising a pair of bearings 66 and 68 separated by a bearingspacer 70. The exact positions of bearings 66 and 68 are determined atone end by a side face 71 of member 65 and a shoulder 72 on the flange52 of shaft 16 against which bearing 68 abuts. The inner race of bearing66 is held in firm position by a retainer ring 74 which snaps into agroove formed on the outer surface of shaft 16. The outer race of thebearing is held by a staked portion 76 at the end 14 of housing 12. Itis to be noted that staking as at 76 is for convenience and that thesame result could be achieved by means of a snap ring or by a threadednut screwed onto and locked to housing 12. The bearings 66 and 68 andspacer 70 are all held firmly in position as above described withoutnecessity for shimming any of the parts. This arrangement also serves tokeep annular member 65 tight against bobbin 34 to hold it in engagementwith ring 38. It is essential that the retainer ring 74 be made so thatwhen inserted in the groove in shaft 16 it will provide sufficient axialforce to properlypreload bearings 66 and 68. Preferably it is formedwitha crosssectional bow as shown. However, it also could be wavy like awavy-spring washer or wedged-shaped in cross-section so as to take upall play and eliminate the need for shims.

The end 18 of housing 12 has a reduced inner diameter to provide aportion 79 in which is mounted the output stage of the device. Theoutput stage includes output shaft which is constructed of a suitablenon-magnetic material such as stainless steel. Output shaft 20 ismounted in axial alignment with axis 17 of input shaft 16. Mounted onthe inner wall of housing 12 between bobbin 36 and the portion 79 is aring 84 which is made of magnetic material and serves as a part of thestator of the brake unit. Ring 84 also serves to maintain bobbin 36 inproper position. A cylindrical sleeve armature 85 is mounted in portion79 of the housing in axial alignment with shaft 16. Armature 85 is fixedagainst rotation by, for example, being press fitted into position inportion 79 of the housing. Armature 85 is made of a magnetic materialand serves as a stator pole for the brake unit as will be described.Armature 85 also provides a means for supporting output shaft 20. Theinner end of armature 85 has a bull-nose extension 88 which issubstantially the same as bull-nose extension 61 of the outer portion 56of rotor 50. Armature 85 is disposed in housing 12 so that a radiallyextending space or gap 89 exists between its end surface 87 and theportion 39 of ring 38. The inner end of shaft 20 has an enlargeddiameter cylindrical portion 91. All of shaft 20 including portion 91 ismade of a non-magnetic material such as, for example, stainless steel.

Output shaft 20 is rotatably supported by means of a bearing assemblycomprising a pair of bearings 92 and 94 located between its outersurface and the inner wall of armature 85, the two bearings areseparated from each other by a bearing spacer 98. it is to be noted thatthe number of bearings used may vary depending upon what is required tosupport the external load applied to shaft 20 (the same thing is truewith respect to the bearings supporting shaft 16). The inner race ofbearing 92 engages a shoulder 100 which is an integral part of shaft 20,while its outer race engages a shoulder 101 on the back side ofbull-nose extension 88 of sleeve armature 85. The inner race of bearing94 is held in firm position by a retainer ring 102 which snaps into agroove formed on the outer surface of shaft 20, while its outer race isheld against axial movement by a staked portion 104 on the outer end ofarmature 85. The staking at 104 could be omitted and the same resultachieved by means of a retaining ring mounted in armature or a nutscrewed onto and locked to the end of armature 85. Retainer ring 102 isof the same type as ring 74 and could be replaced by some other meanssuch as a nut if the end of shaft 20 were threaded. Bearings 92 and 94and bearing spacer 98 are all firmly held in position as shown withoutnecessity for shirnrning any of the parts.

Affixed to the peripheral surface of cylindrical portion 91 of shaft 20is a coupling member 106 which is L-shaped in longitudinal section.Member 106 is made of magnetic material and functions as both part ofthe clutch unit and the brake unit as will be explained. Member 106 iscoaxial with shaft 20 and comprises tow integrally formed portions, anaxially extending hollow, cylindrical portion 107 and a radiallyextending annular portion 108. Annular portion 108 extends from an end109 of cylindrical portion 107 substantially orthogonally with respectto cylindrical portion 107 and axis 17. Although annular portion 108 isshown as being disposed at exactly with respect to and extending awayfrom axis 17, it should be understood that portion 108 may be disposedat some other angle with respect to the axis other than exactly 90.Member 106 may be stamped or drawn and may be affixed to cylindricalportion 91 of shaft 20 by press fitting, welding, brazing, inductivesoldering, staking, or in any other suitable manner. Cylindrical portion107 of member 106 extends into the axial gap 64 between and spaced fromthe inner and outer portions 54 and 58 of rotor 50. Cylindrical portion107 serves as part of the clutch unit in that it rotates together withrotation of input shaft 16 and rotor 50 when coil 30 is energized toestablish a magnetic field as hereinafter described. Annular portion 108of member 106 extends into the radial gap 89 between and spaced from theend surface 87 of sleeve armature 85 and the projection 39 of ring 38.This annular portion 108 serves as part of the brake unit in that itremains fixed against rotation and is magnetically coupled to outputshaft 20 when coil 32 is energized to establish a magnetic, field ashereinafter described.

The axial gap 64 and the radial gap 89 define a single con tinuous spacewhich is'filled with dry magnetic particles 110. Radial gap 89 is fixedin size by the relative dimensioning of the associated components. Theextent to which annular portion 108 of member 106 extends into radialgap 89 is also substantially fixed by the relative dimensioning of theassociated components. The amount that the cylindrical portion 107 ofmember 106 extends into axial gap 64 is not especially critical and mayvary by as much as 10 percent or more without any substantial change intorque.

Although prior art combination clutch and brake assemblies with separateclutch and'brake gaps, only two seals modules generally require fourmembers for sealing the clutch and brake gaps, only two seals 114 and 116 of simple construction are required for sealing the single continuousspace defined by gaps 64 and 89 to prevent the escape of magneticparticles 110. Seals 114 and 116 are simple washers which may be made ofa suitable resilient sealing material such as rubberorplastic-impregnated felt. Washer seal-114 is positioned and confinedradially in a groove 118 in the inner wall of ring 38 and is pressedaxially against the adjacent surface of projection 39 of ring 38 by thebull-nose extension 61 of rotor 50. The rounded end of bull-nose 61compresses washer seal 114 with sufficient force to provide a good sealagainst escape of magnetic particles with minimal drag imparted to therotation of rotor 50. Washer seal 1 16 is pressed axially againstenlarged cylindrical portion 91 of shaft 20 and radially is confinedbetween the cylindrical portion 107 of member 106 and the section ofshaft 20 immediately adjacent portion 91. The

rounded end of bull-nose extension 88 of armature 85 compresses washer116 axially with sufficient force to provide a good seal against escapeof magnetic particles 110 with minimal drag imparted to the rotation ofoutput shaft 20. As mentioned earlier the preferred shape of the end ofbull-nose extensions 61 and 88 is rounded since the smaller the surfacearea engaging the washer seals, the less the rotational drag. However,various other end configurations for the bull-nose extensions would alsobe operative.

As noted above, the ring 38, annular member 65, ring 84, and sleeve 33are all made of magnetic material. These members may be of solidconstruction or may be laminated to reduce eddy currents. As analternative measure, the housing 12 may be made of magnetic material, inwhich case one or more of the foregoing magnetic members could beintegral parts of the housing.

Operation of the above-described device will now be explained. When coil30 is energized via leads 42, a magnetic field is established across theparticles 110 in axial gap 64 through the annular member 65, sleeve 33,ring 38, rotor member 58, cylindrical portion 107 of coupling member106, extension 54 of shaft 16, and flange 52 of shaft 16. With such fluxlinkage across the particles 110, the latter will lock in chains betweenrotor member 58, the cylindrical portion 107 of coupling member 106 andextension 54 of shaft 16, thereby coupling the input shaft 16 to outputshaft 20. The transmitted torque is controllable by varying the strengthof the magnetic field. Once the clutch unit is operating as describedabove, if it is desired to brake the rotation of output shaft 20, coil30 is deenergized while coil 32 via leads 44 is simultaneouslyenergized. With energization of coil 32 a magnetic field is establishedacross the particles 110 in radial gap 89 through ring 38, sleeve 33,ring 84, armature 85 and the annular portion 108 of coupling member 106.The flux linkage across particles 110 will cause them to lock in chainsbetween armature 85, annular portion 108 of coupling member 106, andring 38, whereby output shaft 20 is braked. The clutch and brake unitsboth have very fast response, making the device suitable for fastresponse applications as, for example, magnetic tape drive units, andmini-computer peripheral equipment.

In the embodiment shown in FIG. 1 the cylindrical portion 107 ofcoupling member 106 serves as part of the clutch unit and the annularportion 108 of coupling member 106 serves as part of the brake unit.However, it also is possible, as shown in FIG. 2, to construct theclutch-brake device so that the cylindrical portion of the couplingmember serves as part of the brake unit and the annular portion servesas part of the clutch unit.

FIG. 2 shows a combination magnetic particle clutch and brake assembly200 which includes a cylindrical housing 212 made of nonmagneticmaterial. One portion 214 of housing 212 has a reduced internal diameterso as to provide a shoulder 216. Staked at 218 at the left end ofhousing 212 is a base 220 which has an outer side wall 224, an innerconcentric side wall 226 and an end wall 227. Base 220 is made ofmagnetic material and serves as an armature or stator pole for the brakeunit as will be described. Positioned between side walls 224 and 226 andagainst end wall 227 is a brake driver coil 228 which is wound around abobbin 229 made of an electrical insulating material. Located in fixedposition on the inside surface of outer side wall 224 is an annular ring230 made of magnetic material which serves as a stator pole. Stator pole230 and inner side wall 226 define an axial space or gap 231therebetween. Side walls 224 and 226 are axially positioned with respectto an axis of rotation 233 around which cylindrically shaped input andoutput shafts 232 and 234 respectively rotate. Input and output shafts232 and 234 are concentrically located and spaced from one another.

The inner end of input shaft 232 has both an enlarged diameter section246 which provides an outside shoulder 248 and an inside shoulder 301.This section 246 also has a bullnose extension 250 which is identical tothe bull-nose extensions described in FIG. 1. Input shaft 232 is made ofmagnetic material and serves as a rotor for the clutch unit of assembly200. The clutch unit also includes a rotor cap 252 which is a magnetic,annular member having an axial portion 254, and a radially extendingportion 256. Radially extending portion 256 projects outwardly away fromaxis 233 and axial portion 254 is connected to shaft 232 by anonmagnetic spacer 258 which may be press fitted to hold portion 254 andshaft 232 in fixed relation with respect to one another to define aradial space or gap 259 therebetween. On the left end of axial portion254 or cap 252 is a bull-nose extension 257. Shaft 232 and cap 252rotate together as a unit serving as the entire rotor assembly for theclutch unit. A stator ring 260 is provided for the clutch unit and ismade of magnetic material. Stator 260 is positioned within and securedto housing 212 and has an axially extending cylindrical portion 262which may be'press-fitted on the inside wall of housing 12 and a radial,inwardly extending annular portion 264 which abuts shoulder 216 ofhousing 212. Radial portion 264 of stator 260 is spaced from andconcentric with enlarged portion 246 of input shaft 232. Mounted withinstator ring 260 is a clutch driver coil 270 wound around a bobbin 274similar to bobbin 229. Bobbin 272 may be secured in place by variousmeans, preferably by means of a press fit with respect to stator ring260.

lnput shaft 232 is hollow and is rotatably supported inside housing 212by a bearing assembly located between it and the inside surface ofportion 214 of the housing. This bearing assembly includes a pair ofbearings 274 and 276 which are spaced apart by a bearing spacer 278. Theouter race of bearing 274 bears against radial portion 264 of statorring 260 while the inner race abuts shoulder 248 of shaft 232. Bearing276 and spacer 278 are held in position by a retainer ring 280, which issnapped into a groove in the outer surface of shaft 232, and a stakedportion 282 at the end of portion 214 of housing 212.

Output shaft 234 has an outer end 288 which extends beyond outer end ofinput shaft 232. The inner end of shaft 234 has an enlarged diametercylindrical portion 290. All of shaft 234 including portion 290 is madeof a suitable nonmagnetic material such as stainless steel. Output shaft234 is rotatably supported within input shaft 232 by means of a bearingassembly comprising a pair of bearings 292 and 294 separated from eachother by a bearing spacer 298. It is to be noted that the number ofbearings used to support shafts 232 and 234 may vary depending upon whatis required to support the external loads applied thereto. The innerrace of bearing 292 engages a shoulder 300 which is in integral part ofshaft 234 adjacent portion 290, while its outer race engages theinternal shoulder 301 of shaft 232. The inner race of bearing 294 isheld in firm position by a retainer ring 302 which snaps into a grooveformed on the outer surface of shaft 234, while its outer race is heldagainst axial movement by a staked portion 304 on the outer end of shaft232. The staking at 204 could be omitted and the same result achieved bymeans of a retaining ring mounted in shaft 232 or a nut screwed onto andlocked to the end of shaft 232. Retainer ring 302 is of the same type asring 280 and could be replaced by some other means such as a nut if theend of shaft 234 were threaded. Bearings 292 and 294 and bearing spacer298 are all firmly held in position between shoulder 300 and shoulder301 at one end and retainer ring 302 and staked portion 304 at the otherend without necessity for shimming any of the parts.

Mounted on the periphery of cylindrical portion 290 of shaft 234 is asingle coupling member 306 which is L-shaped in cross-section. Member306 is made of magnetic material and functions as both part of theclutch unit and the brake unit as will be explained. Member 306comprises tow integrally formed portions, an axially extending hollow,cylindrical portion 307, which has an axis of rotation substantiallycoincidental with axis 233, and a radially extending annular portion308. Although annular portion 308 is shown as being disposed at exactlywith respect to and extending away from axis 233, it should beunderstood that portion 308 may be disposed at some other angle withrespect to the axis other than exactly 90. Member 306 may be stamped ordrawn and may be affixed to cylindrical portion 290 of shaft 234 bypress fitting, welding, brazing, inductive soldering, staking or in anyother suitable manner. Cylindrical portion 307 of member 306 extendsinto the axial gap 231 in spaced coaxial relation with stator pole 230and the inner side wall 226 of base 220, and thus serves as part of thebrake unit when brake coil 228 is energized Annular portion 308 ofmember 306 extends into radial gap 259 in spaced relation to section 246of shaft 252 and rotor cap 252. Annular portion 308 serves as part ofthe clutch unit in that it serves to couple input shaft 232 to outputshaft 234 when clutch driver coil 270 is energized.

Axial gap 231 and radial gap 259 define a single continuous space whichis filled with dry magnetic particles 310. Radial gap 259 is fixed insize by the relative dimensioning of the associated components. Theextend to which annular portion 308 of member 306 extends into radialgap 259 is also substantially fixed by the relative dimensioning of theassociated components and no shimming is required. The amount that thecylindrical portion 307 of member 306 extends into axial gap 231 is notcritical and may vary by as much as 10 percent or more without anysubstantial change in torque.

Although prior art combination clutch and brake assemblies with separateclutch and brake modules generally require four members for sealing theclutch and brake gaps, only two seals 314 and 316 of simple constructionare required for sealing the single continuous space defined by gaps 231and 259 to vent escape of magnetic particles 310. Seals 314 and 316 aresimple washers which may be made of a suitable resilient sealingmaterial such as rubber or plastic-impregnated felt. Washer seal 314 ispositioned and confined radially by the inner surface of outer side wall224 of base 220 and is pressed axially against one side surface of pole230 by bull-nose extension 257 of rotor cap 252. The rounded end ofbull-nose 257 compresses washer seal 314 axially with sufficient forceto provide a good seal to substantially prevent escape of mag neticparticles 310 with minimal drag imparted to the rotation of shaft 232and rotor cap 252. Washer seal 316 is pressed axially against enlargedcylindrical portion 290 of shaft 234 and radially is confined betweencylindrical portion 307 of member 306 and the section of shaft 234immediately adjacent portion 290. The rounded end of bull-nose extension250 compresses washer 316 axially with sufficient force to provide agood seal to substantially prevent the escape of magnetic particles 3ll0with minimal drag imparted to the rotation of output shaft 234. Asmentioned earlier the preferred shape of the end of bull-nose extensions250 and 257 is rounded, since the smaller the surface area engaging thewasher seals, the less the rotational drag. However, other endconfigurations for the bull-nose extensions would also be operative.

The operation of the assembly 200 shown in FIG. 2 is substantially thesame as that shown in FIG. 1 except for the fact that the annularportion 308 of member 306 serves as part of the clutch unit as describedwhile the cylindrical portion 307 of member 306 serves as part of thebrake unit as described. Energizing coil 270 establishes magnetic fluxthrough stator ring 260, rotor cap 252, the magnetic particles 310,annular portion 308 of magnetic coupling member 306 and shaft 232, withthe result that output shaft 234 is magnetically clutched to shaft 232.When coil 270 is deenergized and coil 228 is energized, a magnetic fluxcircuit is established through the walls of base 220, stator ring 230,magnetic particles 310 and the cylindrical portion 307 of couplingmember 306, with the result that output shaft 234 is magneticallycoupled to the base and, since the base cannot rotate relative to thehousing, shaft 234 is braked against movement while shaft 232 is stillfree to rotate.

It is to be noted that seal 1 14 is sized so as to be frictionallygripped by member 38 and seal 116 is sized so as to be frictionallygripped by members 91, 106 and 20, so'that the bullnosed sections 61 and88 will rotate relative to them. Seal 314 is similarly gripped by member224 and seal 316 by members 290, 306 and 234. The seals also may befixedly attached to such members by a cement or other suitable fasteningmeans.

It is to be understood that the invention is not limited in itsapplication to the details of construction and arrangement of partsspecifically shown or described and that within the scope of theappended claims, it may be practiced otherwise than as specificallyshown or described.

What is claimed is:

1. A magnetic particle clutch-brake device comprising:

a rotatable shaft having a single magnetic coupling member mountedthereon for rotation therewith, said member comprising a hollowcylindrical portion that is coaxial with said shaft and an annularportion that extends radially of said cylindrical portion;

a brake unit including a stationary magnetic armature and one of saidportions of said coupling member;

a clutch unit including a rotor and a stator and the other of saidportions of said coupling member, said rotor being rotatable withrespect to said stator and said stator being stationary relative to saidarmature;

a first drive coil for establishing magnetic .flux through said armatureand said one portion of said coupling member, said first drive coilbeing held stationary with respect to said armature;

a second drive coil for establishing magnetic flux through said rotorand stator and said other portion of said coupling member, said seconddrive coil being held stationary with respect to said stator;

said coupling member disposed so as to provide a first space betweensaid one portion thereof and said armature and a second space betweensaid other portion thereof and said rotor, said spaces being filled withmagnetic particles; and

sealing means for substantially preventing said magnetic particles fromescaping from said space.

2. A device as set forth in claim 1 wherein said spaces communicate witheach other to form a single large space.

3. A device as set forth in claim 1 wherein:

said brake unit includes said annular portion of said member; and saidclutch unit includes said cylindrical portion of said member. I v

4. A device as set forthin claim 1 wherein:

said brake unit includes said cylindrical portion of said member; andsaid clutch unit includes said annular portion of said member.

5. A device as set forth in claim 1 wherein said coupling member isL-shaped in longitudinal section, and said cylindrical portion forms thelongest leg of said L-shaped section.

6. A device as set forth in claim 1 wherein said annular portion is atone end of said cylindrical portion.

7. A device according to claim 1 wherein the outer diameter of saidannular portion is greater than the outer diameter of said cylindricalportion.

8. A device as set forth in claim 1 wherein said annular portion ispositioned substantially orthogonally with respect to saidaxis ofrotation.

9. A device as set forth in claim 2 wherein said sealing means comprisesonly two sealing members for completely sealing said space.

10. A device as set forth in claim 9 wherein one of said sealing membersengages said rotor and the other of said sealing members engages saidarmature.

11. A device as set forth in claim 9 wherein each of said sealingmembers comprises a compressible washer.

12. A'device as set forth in claim 9 wherein each of said sealingmembers comprises a compressible washer with one of said washers beingpressed between a portion of said rotor and a portion of said armatureand the other of said washers is pressed' between a portion of saidrotor, said shaft, and said coupling member.

13. In a combination magnetic particle clutch-brake device havingrotatable input and output shafts, a brake unit for braking one of saidshafts including a stationary magnetic armature, a clutch unit forclutching said shafts together including a rotor which forms part of oneof said shafts and a stator within which said rotor is rotatablymounted, said stator being stationary with respect to said armature, andfirst and second energizeable coils for generating magnetic flux foroperating said brake and clutch units respectively, said coils beingstationary with respect to said armature and stator, the improvementscomprising:

a single magnetic coupling member mounted on the other of said shaftsfor rotation therewith, said coupling member comprising an annularportion and a cylindrical portion,

said armature and said rotor being spaced from and cooperating with saidcoupling member so as to define a space therebetween,

magnetic particles in said space,

said first coil and one portion of said coupling member being disposedso that when energized said first coil will establish one magnetic fluxpath via said particles through said armature and said one portion ofsaid coupling member for braking said other shaft, and said second coiland the other portion of said coupling member being disposed so thatwhen energized said second coil will establish another magnetic fluxpath via said particles through said rotor and stator and said otherportion of said coupling member so as to clutch said shafts to oneanother, and

means for sealing said space to substantially prevent said magneticparticles from escaping from said space.

14. A combination magnetic particle clutch and brake device comprising:

a rotatable shaft having a single magnetic coupling member mountedthereon for rotation therewith, said member comprising a hollowcylindrical portion that is coaxial with said shaft and an annularportion that extends radially of said cylindrical portion;

a brake unit including a stationary magnetic armature and one of saidportions of said coupling member, said armature having a bull-nosedportion;

a clutch unit including a rotor and a stator and the other of saidportions of said coupling member, said stator being stationary relativeto said armature and said rotor having a bull-nosed portion;

a first drive coil for establishing magnetic flux through said armatureand said one portion of said coupling member;

a second drive coil for establishing magnetic flux through said rotorand stator and said other portion of said coupling member;

said coupling member disposed so as to provide a first space betweensaid one portion thereof and said armature and a second space betweensaid other portion thereof and said rotor, said spaces being filled withmagnetic particles; and

two sealing washers, one of said washers being compressed against aportion of said stator by said bull-nosed portion of said rotor and theother of said washers being pressed against a portion of said shaft anda portion of said member by said bull-nosed portion of said armature,said sealing washers serving to completely seal said space to preventthe escape of said magnetic particles from said space 15. A magneticparticle clutch-brake device comprising:

a housing;

an input shaft and an output shaft each rotatably supported within saidhousing;

a clutch unit for clutching said shafts together, said clutch unitincluding a magnetic rotor on and rotatable with one of said shafts andmeans in said housing defining a magnetic stator in spaced surroundingrelation to said rotor, said rotor having a pair of spaced poles;

a brake unit for braking the other of said shafts, said brake unitincluding means in said housing defining a stationary magnetic core witha pair of spaced poles;

a magnetic coupling member carried by and rotatable with said othershaft, said coupling member comprising a first portion extending betweenand spaced from the poles of said rotor and a second portion extendingbetween and spaced from the poles of said core;

magnetic particles in the spaces between said coupling member and thepoles of said rotor and said core;

sealingmeans for preventing escape of said magnetic particles from saidspaces;

a first coil mounted to said stator for establishing magnetic fluxthrough said stator, said rotor poles, said first portion of saidcoupling member and said particles so as to clutch said shafts to oneanother; and

a second coil mounted to said core for establishing magnetic fluxthrough said core poles, said second portion of said coupling member andsaid particles so as to brake said other shaft.

16. A magnetic particle clutch-brake device according to claim 15wherein the members of one of said pairs of poles are spaced axially ofsaid housing and the members of the other of said pairs of poles arespaced radially of said housing.

17. A magnetic particle clutch-brake device according to claiml5-wherein one shaft is hollow and said other shaft is rotatably mountedwithin said one shaft.

18. A device as set forth in claim 14 wherein: said bull-nosed portionseach has a substantially rounded end which bears against thecorresponding washer with suflicient force to seal said space againstparticle escape while permitting said rotor to rotate. As is apparentfrom the preceding discussion, the applicant's unique acoustic beaconproduces (I) a short pulse at a single frequency, (2) an interval ofsignal at two precisely spaced single frequency components, and (3) aninterval of silence. This signal has been found to have characteristicswhich make it particularly well suited for use in a highly accurateacoustic position reference system. Although a specific embodiment ofapparatus for producing the specified signal is shown for illustrativepurposes, other embodiments which do not depart from the applicantscontemplation and teaching will be apparent to those skilled in the art.The applicant does not wish to be limited to the disclosed embodiment,but only by the terms of the appended claims.

I claim:

1. An acoustic beacon for transmitting a periodic amplitude modulatedsignal comprising:

modulator means operable to produce a signal characterized by a firstfrequency amplitude modulated by a second frequency;

timer means connected to said modulator means and operable toperiodically interrupt modulation of the first frequency so that saidmodulator means produces a periodic output signal, each period of whichcomprises a first interval of the first frequency followed by a secondinterval of the first frequency modulated by the second frequency;

acoustic projector means; and

driving means connected to said modulator means and said acousticprojector means so as to energize said acoustic projector means inresponse to the periodic output signal.

2. The beacon of claim 1 wherein said timer means includes means forperiodically blanking the output of said modulator means so that eachperiod of the output signal produced thereby includes a third intervalof silence, whereby said acoustic projector is caused to transmit aperiodic acoustic signal in which each period successively comprises afirst interval of the first frequency, a second interval of the firstfrequency modulated by the second frequency and a third interval ofsilence.

3. Signal modulation apparatus for use in an acoustic beacon comprising:

a first oscillator for producing a first signal having a frequency 1",;a second oscillator for producing a second signal having a frequency f amodulator connected to said first and second oscillators so as toreceive the first and second signals therefrom, said whose predominantfrequency components are f, -f, and f1 f2- 4. The apparatus of claim 3wherein said timer means is operable to periodically blank the signalproduced by said modulator so that each period of the modulated signalincludes a third interval of silence.

1. A magnetic particle clutch-brake device comprising: a rotatable shafthaving a single magnetic coupling member mounted thereon for rotationtherewith, said member comprising a hollow cylindrical portion that iscoaxial with said shaft and an annular portion that extends radially ofsaid cylindrical portion; a brake unit including a stationary magneticarmature and one of said portions of said coupling member; a clutch unitincluding a rotor and a stator and the other of said portions of saidcoupling member, said rotor being rotatable with respect to said statorand said stator being stationary relative to said armature; a firstdrive coil for establishing magnetic flux through said armature and saidone portion of said coupling member, said first drive coil being heldstationary with respect to said armature; a second drive coil forestablishing magnetic flux through said rotor and stator and said otherportion of said coupling member, said second drive coil being heldstationary with respect to said stator; said coupling member disposed soas to provide a first space between said one portion thereof and saidarmature and a second space between said other portion thereof and saidrotor, said spaces being filled with magnetic particles; and sealingmeans for substantially preventing said magnetic particles from escapingfrom said space.
 2. A device as set forth in claim 1 wherein said spacescommunicate with each other to form a single large space.
 2. The beaconof claim 1 wherein said timer means includes means for periodicallyblanking the output of said modulator means so that each period of theoutput signal produced thereby includes a third interval of silence,whereby said acoustic projector is caused to transmit a periodicacoustic signal in which each period successively comprises a firstinterval of the first frequency, a second interval of the firstfrequency modulated by the second frequency and a third interval ofsilence.
 3. Signal modulation apparatus for use in an acoustic beaconcomprising: a first oscillator for producing a first signal having afrequency f1; a second oscillator for producing a second signal having afrequency f2; a modulator connected to said first and second oscillatorsso as to receive the first and second signals therefrom, said modulatorbeing operable to produce a modulated signal whose predominant frequencycomponents are f1 - f2 and f1 + f2; and timer means connected to saidmodulator for periodically interrupting modulation of the first signal,whereby said modulator produces a periodic output signal, each period ofwhich comprises a first interval of signal whose frequency is f1followed by a second interval of signal whose predominant frequencycomponents are f1 - f2 and f1 + f2.
 3. A device as set forth in claim 1wherein: said brake unit includes said annular portion of said member;and said clutch unit includes said cylindrical portion of said member.4. A device as set forth in claim 1 wherein: said brake unit includessaid cylindrical portion of said member; and said clutch unit includessaid annular portion of said member.
 4. The apparatus of claim 3 whereinsaid timer means is operable to periodically blank the signal producedby said modulator so that each period of the modulated signal includes athird interval of silence.
 5. A device as set forth in claim 1 whereinsaid coupling member is L-shaped in longitudinal section, and saidcylindrical portion forms the longest leg of said L-shaped section.
 6. Adevice as set forth in claim 1 wherein said annular portion is at oneend of said cylindrical portion.
 7. A device according to claim 1wherein the outer diameter of said annular portion is greater than theouter diameter of said cylindrical portion.
 8. A device as set forth inclaim 1 wherein said annular portion is positioned substantiallyorthogonally with respect to said axis of rotation.
 9. A device as setforth in claim 2 wherein said sealing means comprises only two sealingmembers for completely sealing said space.
 10. A device as set forth inclaim 9 wherein one of said sealing members engages said rotor and theother of said sealing members engages said armature.
 11. A device as setforth in claim 9 wherein each of said sealing members comprises acompressible washer.
 12. A device as set forth in claim 9 wherein eachof said sealing members comprises a compressible washer with one of saidwashers being pressed between a portion of said rotor and a portion ofsaid armature and the other of said washers is pressed between a portionof said rotor, said shaft, and said coupling member.
 13. In acombination magnetic particle clutch-brake device having rotatable inputand output shafts, a brake unit for braking one of said shafts includinga stationary magnetic armature, a clutch unit for clutching said shaftstogether including a rotor which forms part of one of said shafts and astator within which said rotor is rotatably mounted, said stator beingStationary with respect to said armature, and first and secondenergizeable coils for generating magnetic flux for operating said brakeand clutch units respectively, said coils being stationary with respectto said armature and stator, the improvements comprising: a singlemagnetic coupling member mounted on the other of said shafts forrotation therewith, said coupling member comprising an annular portionand a cylindrical portion, said armature and said rotor being spacedfrom and cooperating with said coupling member so as to define a spacetherebetween, magnetic particles in said space, said first coil and oneportion of said coupling member being disposed so that when energizedsaid first coil will establish one magnetic flux path via said particlesthrough said armature and said one portion of said coupling member forbraking said other shaft, and said second coil and the other portion ofsaid coupling member being disposed so that when energized said secondcoil will establish another magnetic flux path via said particlesthrough said rotor and stator and said other portion of said couplingmember so as to clutch said shafts to one another, and means for sealingsaid space to substantially prevent said magnetic particles fromescaping from said space.
 14. A combination magnetic particle clutch andbrake device comprising: a rotatable shaft having a single magneticcoupling member mounted thereon for rotation therewith, said membercomprising a hollow cylindrical portion that is coaxial with said shaftand an annular portion that extends radially of said cylindricalportion; a brake unit including a stationary magnetic armature and oneof said portions of said coupling member, said armature having abull-nosed portion; a clutch unit including a rotor and a stator and theother of said portions of said coupling member, said stator beingstationary relative to said armature and said rotor having a bull-nosedportion; a first drive coil for establishing magnetic flux through saidarmature and said one portion of said coupling member; a second drivecoil for establishing magnetic flux through said rotor and stator andsaid other portion of said coupling member; said coupling memberdisposed so as to provide a first space between said one portion thereofand said armature and a second space between said other portion thereofand said rotor, said spaces being filled with magnetic particles; andtwo sealing washers, one of said washers being compressed against aportion of said stator by said bull-nosed portion of said rotor and theother of said washers being pressed against a portion of said shaft anda portion of said member by said bull-nosed portion of said armature,said sealing washers serving to completely seal said space to preventthe escape of said magnetic particles from said space.
 15. A magneticparticle clutch-brake device comprising: a housing; an input shaft andan output shaft each rotatably supported within said housing; a clutchunit for clutching said shafts together, said clutch unit including amagnetic rotor on and rotatable with one of said shafts and means insaid housing defining a magnetic stator in spaced surrounding relationto said rotor, said rotor having a pair of spaced poles; a brake unitfor braking the other of said shafts, said brake unit including means insaid housing defining a stationary magnetic core with a pair of spacedpoles; a magnetic coupling member carried by and rotatable with saidother shaft, said coupling member comprising a first portion extendingbetween and spaced from the poles of said rotor and a second portionextending between and spaced from the poles of said core; magneticparticles in the spaces between said coupling member and the poles ofsaid rotor and said core; sealing means for preventing escape of saidmagnetic particles from said spaces; a first coil mounted to said statorfor establishing magNetic flux through said stator, said rotor poles,said first portion of said coupling member and said particles so as toclutch said shafts to one another; and a second coil mounted to saidcore for establishing magnetic flux through said core poles, said secondportion of said coupling member and said particles so as to brake saidother shaft.
 16. A magnetic particle clutch-brake device according toclaim 15 wherein the members of one of said pairs of poles are spacedaxially of said housing and the members of the other of said pairs ofpoles are spaced radially of said housing.
 17. A magnetic particleclutch-brake device according to claim 15 wherein one shaft is hollowand said other shaft is rotatably mounted within said one shaft.
 18. Adevice as set forth in claim 14 wherein: said bull-nosed portions eachhas a substantially rounded end which bears against the correspondingwasher with sufficient force to seal said space against particle escapewhile permitting said rotor to rotate. As is apparent from the precedingdiscussion, the applicant''s unique acoustic beacon produces (1) a shortpulse at a single frequency, (2) an interval of signal at two preciselyspaced single frequency components, and (3) an interval of silence. Thissignal has been found to have characteristics which make it particularlywell suited for use in a highly accurate acoustic position referencesystem. Although a specific embodiment of apparatus for producing thespecified signal is shown for illustrative purposes, other embodimentswhich do not depart from the applicant''s contemplation and teachingwill be apparent to those skilled in the art. The applicant does notwish to be limited to the disclosed embodiment, but only by the terms ofthe appended claims. I claim: